Sending designs back and forth via email for feedback is so old fashioned now. Besides being messy and unorganized, it also consumes a lot of time. TheCommentor is a web tool that lets users collaborate and discuss design mockups on the web without emailing each other anything.

Once you sign up for a free account, you can invite up to 3 users to post comments on your sketches and drawings. They can leave a comment, post a reply to a comment, do some basic editing and switch between different versions of a design. The group administrator can manage rights for all users, give them access or even remove them from a group. A list of projects and list of designs within each project makes it easy to organize stuff.